The present invention relates to a magnetic recording medium having a back-coat layer, which is excellent in running durability, antistatic property and light screening property.
A magnetic recording medium, in particular, a video tape and an audio tape is preferably provided with a back-coat layer in order to stabilize the running property, suppress static electrification, suppress the wear of the tape by means of a fixing pin and optically detect the position. There are two methods for forming a back-coat layer. One is a method of forming a back-coat layer simultaneously with or subsequently to the steps of applying a magnetic layer to a biaxially stretched polyester film, orienting and drying it, and the other is a method of forming a back-coat layer in the re-coating process after the formation of the magnetic layer. Both of these methods, however, have problems. Since the coating of the magnetic layer or the back-coat layer is required to have accuracy, when the coating of the magnetic layer and the back-coat layer is carried out simultaneously or continuously, the yield is lowered. While if the coatings of those layers are carried out in separate processes, the manufacturing cost is raised.
The back-coat layer is required to have various properties. A polyester film obtained by an in-line coating method is required to have an excellent winding property and to exhibit excellent running property, winding property and running durability after it is formed into a magnetic tape.
The present inventors fixed their eyes on the in-line coating method which is capable of producing a stretched film having an accurate coating layer with good adhesion with the base film at a comparatively low cost, and studied a method of forming a back-coat layer of a magnetic recording medium. As a result, it has been found that a magnetic recording medium comprising a polyester film provided with a coating-type magnetic layer on one side thereof and a back-coat layer formed by an in-line coating method on the other side thereof is excellent in running durability, antistatic property and light screening property. The present invention has been achieved on the basis of this finding.